RAH, thanks for the input.
Yes, my soil profile and lateral heterogeneity appear to be highly variable, based upon my sparse sampling.
I have hit some sand veins that were 2' thick. I have also failed to reach good clay in some of my holes. (However, I could only get down about 8.5' with the mini-excavator.)
There are "wet spots" in our prairie grass areas that have sedges and willow trees growing amongst the grasses. I am pretty sure those areas have a solid clay layer below the permeable soils. I have hit solid wet clay in all of the test pits in those areas.
However, running a dozer and excavator combo on wet clay at the bottom of the hole is going to add a significant amount of time/money to the pond excavation.
I am hoping to have some basal clay in the drier areas, but that might be the reason they are drier!
I am pretty sure my project will be like your first three ponds - I am going to have to seal off some sand veins. I am just trying to make sure I have the materials at the excavation site to accomplish that goal!
P.S. How far apart are your three ponds? I think you watched the excavation in a few of yours. How much variability did you observe in the "bowl" of your ponds before the dirt guys started re-distributing the material?
